caMOD - Cancer Models Database

The p53 tumor suppressor gene is mutated in a large percentage of human malignancies including tumors of the colon, breast, lung and brain. Individuals who inherit one mutant allele of p53 are susceptible to a wide range of tumor types. The gene encodes a transcriptional regulator that may function in the cellular response to DNA damage. The construction of mouse strains carrying germline mutations of p53 facilitates analysis of the function of p53 in normal cells and tumorigenesis. In order to study the effects of p53 mutation in vivo, we have constructed a mouse strain carrying a germline disruption of the gene. p53KO was constructed by cloning fragments of the murine p53 gene (isolated from strain BALB/c) into the targeting vector pPNT. The neo gene in p53KO is flanked by a 3.5 kb fragment extending from the Bam HI site in intron 1 to the NcoI in exon 2 and a 5 kb fragment extending from the Bam HI in intron 6 to the Eco RI downstream of exon 11. Electroporation of p53KO into D3 ES cells, subsequent drug selection, and Southern blot analysis were performed as described. The Southern blot probe A consists of an Eco RI to BsmI fragment of p53 genomic DNA including exon 1; probe B is a SacII to KpnI fragment of p53 cDNA which includes exons 7 through 10. Heterozygous ES cells (derived from strain 129/SV) were injected into C57BL/6 blastocysts. Extensively chimeric males were screened for germline contribution of the mutant cells by breeding to C57BL/6 females. Genotypic analysis was performed by Southern blotting or PCR. The wild-type p53 allele was amplified using PCR primers directed against exon 6 (W5': 5'-ACAGCGTGGTGGTACCTTAT-3') and exon 7 (W3': 5'-TATACTCAGAGCCGGCCT-3'), whereas the p53 allele was amplified using a primer directed against neo (M5': 5'-CTATCAGGACATAGCGTTGG-3') and W3'. Homozygous offspring were generated initially from heterozygous intercrosses and subsequently from homozygous intercrosses. All of these animals are on a 129/SV x C57BL/6 mixed genetic background.

Phenotype

In addition, we have found that mice heterozygous for the p53 mutation are predisposed to cancer. The tumor phenotype of these animals differs from that of homozygotes, both with respect to latency and distribution of tumor types. The longer tumor latency observed in heterozygous mice could be explained by the requirement for heterozygous cells to mutate the wild-type p53 allele at some point during tumorigenesis. Indeed, three quarters of the tumors from p53+/- animals examined here showed loss of the wild-type p53 allele. This result indicates not only that elimination of p53 function is selected for during tumorigenesis, but also that the acquisition of a potentially activating point mutation in the remaining p53 allele is infrequent in this setting. These data are compatible with models in which point-mutated alleles of p53 act predominantly to inhibit the function of wild-type p53 protein. Heterozygous animals also differ from homozygotes in the spectrum of tumors to which they are predisposed, with sarcomas being the most common tumor type observed in heterozygotes rather than the lymphomas of the homozygotes. Given the requirement to mutate the wild-type p53 allele in heterozygotes, an important factor in determining the tumor spectrum in these animals may be the frequency of this mutational event in different tissues. In particular, the relatively slow elimination of the wild-type p53 allele would be expected to limit the frequency of thymic lymphoma in heterozygotes, as the number of immature thymocytes drops dramatically following thymic involution at several weeks of age.

Website for add. info

Breeding Notes

Sex Distribution of the Phenotype

Both Sexes

Submitted by

Jacks, Tyler

Principal Investigator / Lab

Jacks, Tyler

Comment

Model Availability: This model is available from

Strain	Distributor	Stock number
	Jackson Laboratory	002080
	Jacks, Tyler

Comments (Please login to submit new comments)

DISCLAIMER

ACCESSIBILITY

APPLICATION SUPPORT